1. Field of the Invention
The present invention relates to construction and operation of main and distribution networks of pressure and pressure-free pipelines, and more particularly it relates to a method of protecting the internal surface of a pipeline against corrosion and to an apparatus capable of performing this method.
2. Description of the Prior Art
Nowadays the problem of affording protection to the internal surfaces of pipelines has become acute. It is particularly acute in what concerns the protection of the internal surfaces of pipelines either under construction or already in operation without the use of adhesive or cementing substances. As the internal surface of a pipeline is moistened by either the fluid being conveyed, e.g. water, or by dew, this surface has to be dried prior to being coated with a flexible sleeve of the coating material.
The drying of the surface being coated has to conducted immediately before the urging of the protective sleeve against the inner wall of the pipeline, for a surface dried in advance might be moistened once again from the atmospheric air by the moment of the application of the protective coating.
At present, there are known various methods and devices for protecting the internal surface of a pipeline against corrosion, e.g. by employment of a cement-sand mixture such as a plant for applying a cement-sand mixture marketed by Ameron Inc., USA.
A shortcoming of this process is its low productivity, with a single unit being operable within one day only 690 meters of pipeline with the diameter of 700 mm may be coated.
There is known another method of protecting the internal surface of a pipeline, including introducing into the pipeline a flexible sleeve of the coating material, which is urged against the internal surface of the pipeline which has been preheated in advance.
The apparatus for performing this method comprises a system for feeding a working fluid into the pipeline, a system for introducing a flexible sleeve, a device for heating the pipeline, and a system for timing the advance of the sleeve and of the heating device (cf. SU Inventor's Certificate No. 1024653, F16L 58/16, 1980).
These method and apparatus are not suitable for protecting against corrosion of lengthy pipelines either under construction or already in operation, with the protective coating being applied with the employment of heating. This is explained by the fact that in the known apparatus the heating device is in the form of an annular oven mounted in the pipeline. In practice, such an oven would not be moved along an extended pipeline with appropriate timing of the advance of the oven and of the sleeve being introduced into the pipeline.
The abovedescribed apparatus is operated under factory conditions and cannot be used for protection of pipelines laid into the soil or supported on an elevated structure.